In automatic choke controls, a bimetallic coil is commonly utilized and is connected to the automatic choke to tend to hold the choke in closed position when the engine is cold and to tend to open the choke when the engine temperature rises. Such automatic choke controls are shown, for example, in U.S. Pat. No. 3,093,999, 4,050,427, 4,083,336 and 4,038,955. The control may include heaters and other electrical controls associated with the bimetallic coil.
In such choke control systems, if the bimetallic coil tends to cool faster than the engine, a condition is reached where the system provides fast idle and enrichment when it is not required by the engine. Such a condition can occur most often after the engine has been shut off and allowed to cool for 15-60 minutes. The condition tends to be more severe where an electrically heated choke system is provided as contrasted to the air or water heated choke control system.
It has heretofore been suggested that heat sinks be provided in the housing of the choke control, as shown for example, in U.S. Pat. Nos. 4,058,097 and 4,218,406. Such control systems require a specially constructed and designed housing.
Accordingly, among the objectives of the present invention are to provide a choke control system wherein the advantages of a heat sink are achieved without specially designing the choke control housing; which can be adapted to more conventional choke controls without a heat sink and which will effectively provide the desired result at minimal cost.
In accordance with the invention, a body of porous material is provided which is impregnated with a material such as paraffin that is normally solid and becomes liquid at an elevated temperature. The body is retained on the exterior of the choke control housing, preferably by a cap, so that it functions as a heat sink to store thermal energy in the solid material converting the material to a liquid.